I used large rifle primers in my .444/.410 loads and have never tried the Magtech yet. But my .410s are newish ('40s and '50s) and stout. GLSs' caveat might well hold true for an earlier gun.

I had a Peiper hammer "cape gun" with an unchoked 2" Brit "Fourten" .410 chamber on one side, but always used .444 shells loaded with black powder, the few times I fired it. It was made in the 'teens and had fluid steel barrels.